The present invention relates generally to tensioners used with chain drives in automotive timing and power transmission applications. In particular, the present invention is related to a hydraulic chain tensioner device which has an associated oil reservoir. The oil reservoir is formed between a seal cap located in an engine block or mounting block oil supply passage and the tensioner body.
Chain tensioning devices, such as hydraulic tensioners, are used as control devices for power transmission chains as the chain travels between a plurality of sprockets. In an automotive application, the tension of the chain can vary greatly due to the wide variation in the temperature and the linear expansion among the various parts of the engine. Moreover, wear to the chain components during prolonged use can produce a decrease in the tension of the chain. As a result, it is important to impart and maintain a certain degree of tension to the chain to prevent noise, slippage, or unmeshing of the chain with the sprocket teeth. It is especially important in the case of a chain-driven camshaft in an internal combustion engine to prevent the chain from slipping because the camshaft timing can be misaligned by several degrees, possibly rendering the engine inoperative or causing damage.
Hydraulic chain tensioners typically have a plunger slidably fitted into the bore of a housing. The space between the hollow plunger and the housing bore forms an oil or fluid chamber. The plunger is biased in a protruding direction outwardly by a spring located in the fluid chamber to provide tension to an associated chain. A lever arm or shoe is often used at the end of the plunger to assist in the tensioning of the chain. A hydraulic tensioner as used with a tensioner arm or shoe is shown in Simpson et al., U.S. Pat. No. 5,967,921, which is incorporated herein by reference. The hydraulic pressure from an external source, such as an oil pump or the like, flows into the chamber through passages formed in the housing. The plunger is moved outward against the arm and thus, the chain, by the combined efforts of the hydraulic pressure and the spring force.
When the plunger tends to move in a reverse direction (inward) away from the chain, typically a check valve is provided to restrict the flow of fluid from the chamber. In such a fashion, the tensioner achieves a so-called no-return function, i.e., movements of the plunger are easy in one direction (outward) but difficult in the reverse direction. In addition, rack and ratchet mechanisms, which are well known in the art are employed to provide a mechanical no-return function. An example of a hydraulic tensioner including the above conventional features and a no-return mechanism is shown in Tada, U.S. Pat. No. 5,860,881, which is incorporated herein by reference.
Typically, oil pressure in the fluid chamber does not rise immediately upon start-up of the engine. This causes an initial insufficient or low oil pressure condition in the oil chamber acting upon the plunger. Poor control of the chain tension and high noise in the chain and associated mechanisms may result during the initial low oil pressure condition.
A hydraulic tensioner with an oil reservoir, as disclosed in Japanese Laid Open Patent H6/45141, has been proposed to solve such problems. In such a hydraulic tensioner, a hold for the storage of oil, i.e., an oil reservoir, that connects to the oil chamber, is formed in the housing and the oil stored in the oil reservoir is supplied to the fluid chamber in a more timely manner. However, in the conventional hydraulic tensioner with an oil reservoir, due to the need for an oil storage hole in the housing, the housing and overall hydraulic tensioner becomes large compared to the requirement for space saving for the engine. Manufacturing costs are also increased.
A hydraulic tensioner has been disclosed by Japanese Laid-Open Utility Model H7/47631, in which the wall of the hydraulic tensioner, for attachment to the engine, is used as a part of the wall of the oil reservoir. A separate concavity for oil storage is formed in the housing. In this example, the manufacturing cost of the unit is high and the overall hydraulic tensioner becomes large.
In the present invention, a hydraulic tensioner is provided which is less expensive to manufacture and is smaller than conventional hydraulic tensioners while addressing the need for a supplying a ready supply of oil to the tensioner during start-up of the engine.
The hydraulic tensioner of a first embodiment of the present invention includes a hydraulic tensioner for an engine timing chain having a housing and a plunger. The plunger is slidably received in the housing. A seal cap with a C-shaped cross-section having a concavity on its outside surface is mounted at the open end of an oil supply passage provided in the engine block. The concave portion of the seal cap in combination with an outside surface of the tensioner acts as an oil reservoir. An oil passage connects the concavity with an oil chamber formed in the housing. An orifice in the seal cap connects the oil supply passage in the engine block with the concavity formed in the seal cap.
The hydraulic tensioner of this invention utilizes the concavity formed in the seal cap, when mounted on the engine block, so that separate formation of an oil storage hold or a concavity in the tensioner housing is unnecessary, thereby reducing manufacturing costs and preventing an increase in the overall size of the housing, thereby saving space.
Oil is supplied to the oil reservoir which is the outside concave portion of the seal cap via an orifice formed in the seal cap and the oil supply passage in the engine block. Thus, oil from the oil reservoir is retained in the oil chamber in the tensioner housing after shut down on account of the seal cap and thus oil is available in the fluid chamber, even immediately after re-starting the engine.
For a further understanding of the present invention and the objects thereof, attention is directed to the drawing and the following brief description thereof, to the detailed description of the preferred embodiment of the invention and to the appended claims.